Good Friday is the day when many Christians around the world make a special effort to remember the crucifixion of Jesus for our sins. Jesus' death on the cross is the cornerstone of every good work of transformation God has done and is doing in your life and in my life. God forgives our sins--past, present & future because Jesus purchased them by his sacrifice.
I am a living testimony to the work of God in my life in the form of emotional healing from an eating disorder, binge drinking, and many hurts and difficulties of life--as well as the conviction and correction of ongoing sinfulness in my own life.
Our relationship with Jesus does not depend on what we bring to the table but rather what he offers us through the cross. Forgiveness from our sins and eternity in Heaven is ours if we'll just trust in him alone to break down the wall that sin built between us and God.
That's why the day Jesus was crucified can be seen as "good", why this day should receive special observance and why Jesus deserves our devotion all year round.